entry
    \ catch let err :=
        \ await { sys::println 'Number a:' },
        \ await let str-a := { sys::scanln '' },
        \ await { sys::println 'Number b:' },
        \ await let str-b := { sys::scanln '' },
        let sum? :=
            \ Maybe let a := str-a.{NormalFloat?},
            \ Maybe let b := str-b.{NormalFloat?},
            { Some (a + b) },
        switch sum?:
        case Some sum:
            { sys::println { String sum } },
        case None:
            { sys::println 'None' },
        end,
    { crash err };
